1. Field of the Invention
The present invention relates to a semiconductor device using an oxide semiconductor and a method for manufacturing the semiconductor device.
2. Description of the Related Art
There are a variety of kinds of metal oxides intended for many uses. Indium oxide is a well-known material and is used as a transparent electrode material necessary for a liquid crystal display or the like.
Some metal oxides have semiconductor characteristics. For example, tungsten oxide, tin oxide, indium oxide, zinc oxide, and the like can be given as metal oxides which have semiconductor characteristics, and thin film transistors in which a channel formation region is formed using such a metal oxide which has semiconductor characteristics are already known (Patent Documents 1 to 4 and Non-Patent Document 1).
As the metal oxides, not only one-element oxides but also multi-element oxides are known. For example, InGaO3(ZnO)m (m: natural number) having a homologous phase is known as a multi-element oxide semiconductor including In, Ga, and Zn (Non-Patent Documents 2 to 4).
Further, it is proved that the oxide semiconductor formed using an In—Ga—Zn-based oxide as described above can be used for a channel layer of a thin film transistor (Patent Document 5 and Non-Patent Documents 5 and 6).
Further, attention has been drawn to a technique by which a thin film transistor is manufactured using an oxide semiconductor and such a transistor is applied to an electronic device or an optical device. For example, Patent Document 6 and Patent Document 7 disclose a technique by which a thin film transistor is manufactured using zinc oxide or an In—Ga—Zn—O-based oxide semiconductor as an oxide semiconductor film and such a thin film transistor is used as a switching element or the like of an image display device.